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06/09/2018

Interesting!

17/06/2017

CYCLOPLEGIC REFRACTION
The cycloplegic refraction is a cornerstone of the eye exam on young children. “Cyclo” drops, such as cyclopentolate or atropine are a class of drugs called cycloplegics. Cycloplegics paralyze the focusing muscle inside the eye. The focusing muscle inside the eye (ciliary body), when flexed, is able to help the eyes focus at near as well as overcome hyperopia (farsightedness). In children, their focusing muscles are very strong, allowing children to overcome very high amounts of hyperopia. In doing so, the child may test with 20/20 vision, but only because the focusing muscle is working so hard. Over the course of minutes to hours, however, this extra work may cause headaches or blurred vision as the muscle begins to fatigue.

So a child who’s prescription is +4.00, may test at 20/20 vision, can see the board at school well, but complain about headaches, especially when reading (when additional strain is placed upon the focusing muscle). Additionally, the two eyes cannot work independently. So if the prescription is plano in the right eye and +4.00 in the left the child may claim to see just fine, but this is only because they are only using the right eye, many times without even realizing it. The result is the +4.00 left eye never receives a clear image, the nerve pathway is never stimulated to develop, and unless is corrected by about the age of 8 becomes amblyopic (a lazy eye uncorrectable even with glasses)
What a cycloplegic refraction does, then, by paralyzing the focusing muscles of the eye, is allow the doctor to determine the full prescription in each eye without the child’s focusing muscles being able to hide any of it by being in a state of work. Countless times I can recall cases where a child’s “dry” refraction (without the use of cyclo drops) is plano, but because the child’s chief compliant is “headaches when reading” we placed cyclo drops in the eye and suddenly the manifest or retinoscopy refraction reveals the true prescription is +4.00 or higher. Additionally, other cases where the child has no visual complaints, their acuity is 20/20 in the right eye but only 20/60 in the left. “Dry” refraction reveals a prescription of plano in each eye, however when cyclo drops are applied the full true prescription of plano right eye and +4.00 left eye is revealed and suddenly the poor vision in the left eye has an explanation. In this case, a diagnosis of “refractive amblyopia” left eye can be made, and glasses along with a course of vision therapy (usually patching the right eye while wearing glasses to stimulate the lazy left eye to begin development) is initiated.

So, in summary, the cycloplegic refraction helps the doctor determine the full, true, prescription knowing none of it is being hidden by the child’s focusing muscles working overtime.

16/03/2017

Scientists have developed a retinal implant that can restore lost vision in rats, and are planning to trial the procedure in humans later this year.

The implant, which converts light into an electrical signal that stimulates retinal neurons, could give hope to millions who experience retinal degeneration – including retinitis pigmentosa – in which photoreceptor cells in the eye begin to break down, leading to blindness
The retina is located at the back of the eye, and is made up of millions of these light-sensitive photoreceptors. But mutations in any one of the 240 identified genes can lead to retinal degeneration, where these photoreceptor cells die off, even while the retinal neurons around them are unaffected
ecause the retinal nerves remain intact and functional, previous research has looked at treating retinitis pigmentosa with bionic eye devices that stimulate the neurons with lights, while other scientists have investigated using CRISPR gene editing to repair the mutations that cause blindness.

Now, a team led by the Italian Institute of Technology has developed a new approach, with a prosthesis implanted into the eye that serves as a working replacement for a damaged retina.

The implant is made from a thin layer of conductive polymer, placed on a silk-based substrate and covered with a semiconducting polymer.

The semiconducting polymer acts as a photovoltaic material, absorbing photons when light enters the lens of the eye. When this happens, electricity stimulates retinal neurons, filling in the gap left by the eye's natural but damaged photoreceptors.

To test the device, the researchers implanted the artificial retina into the eyes of rats bred to develop a rodent model of retinal degeneration – called Royal College of Surgeons (RCS) rats.

After the rats had healed from the operation 30 days later, the researchers tested how sensitive they were to light – called the pupillary reflex – compared to healthy rats and untreated RCS rats.

At the low intensity of 1 lux – a bit brighter than the light from a full moon – the treated rats weren't much more responsive than untreated RCS rats.

But as the light increased to around 4–5 lux – about the same as a dark twilight sky – the pupillary response of treated rats was largely indistinguishable from healthy animals.

When they retested the rats at six and 10 months after surgery, the implant was still effective in the rats – although all the rats in the tests (including the treated rats, the healthy animals, and the RCS controls) had suffered minor vision impairment due to being older.

Using positron emission tomography (PET) to monitor the rats' brain activity during the light sensitivity tests, the researchers saw an increase in the activity of the primary visual cortex, which processes visual information.

Based on the results, the team concludes that the implant directly activates "residual neuronal circuitries in the degenerate retina", but further research will be required to explain exactly how the stimulation works on a biological level.

"[T]he detailed principle of operation of the prosthesis remains uncertain," they explain in their paper.

While there are no guarantees that the results seen in rats will translate to people, the team is hopeful that it will – and from the sounds of things, it won't be too long until we find out.

"We hope to replicate in humans the excellent results obtained in animal models," says one of the researchers, ophthalmologist Grazia Pertile from the Sacred Heart Don Calabria in Negrar, Italy.

"We plan to carry out the first human trials in the second half of this year and gather preliminary results during 2018. This [implant] could be a turning point in the treatment of extremely debilitating retinal diseases."

19/12/2016

Night blindness (nyctalopia) is a type of vision impairment. People with night blindness experience poor vision at night or in dimly lit environments. Although the term “night blindness” implies that you cannot see at night, this is not the case. You may just have more difficulty seeing and/or driving in darkness.
Some types of night blindness are treatable, and others are not. Consult your doctor to determine the underlying cause of your vision impairment. Once you know the cause of the problem, you can take steps to correct your vision.
The sole symptom of night blindness is difficulty seeing in the dark. You are more likely to suffer from night blindness when transitioning from a bright environment to an area of low light. You are likely to experience poor vision when driving, due to the intermittent brightness of headlights and streetlights on the road.
Genetic conditions that cause night blindness, such as retinitis pigmentosa, are not treatable. The genetic defect that causes pigment to build up in the retina does not respond to corrective lenses or surgery. People suffering from this form of night blindness should avoid driving at night.
Night blindness that is the result of birth defects or genetic conditions, such as Usher syndrome, cannot be prevented. You can, however, properly monitor your blood sugar levels and eat a balanced diet to make night blindness less likely.
Eat foods rich in antioxidant vitamins and minerals, which may help prevent cataracts. Also choose foods that contain high levels of vitamin A to reduce your risk of night blindness. Orange-colored foods are excellent sources of vitamin A, including:
cantaloupes
sweet potatoes
carrots
pumpkins
butternut squash
mangoes
Spinach, collard greens, milk, and eggs also contain vitamin A.